The liquid crystal lens auto-focusing system has several advantages over the conventional mechanical-based auto-focusing systems, which utilize a plurality of mechanical moving parts so as to provide auto focusing, such as, for example, the ability to perform electrical tuning, having lower cost, lower power consumption, having simpler fabrication requirement, lighter weight, and reduced module height. Nevertheless, the conventional CCM module auto-focusing system possesses a plurality of disadvantages as well, such as: being polarization dependent, having slower response time, requiring relatively higher driving voltage, having the image quality dependent upon the applied voltage, having relatively smaller aperture size of less than 5 mm, and providing inadequate lens power.
To improve upon the performance of the conventional liquid crystal layer in providing image focusing for image capturing systems, the following have been attempted in the past including, for example: 1) cutting the liquid crystal layer into multiple layers so as to reduce the cell thickness of each liquid crystal layer to thereby achieve a faster liquid crystal response time at the same time, without having any net effect upon the lens power of the liquid crystal lens. However, this method has the disadvantages of having a complicated structure and is prone to damages; and 2) using a complicated voltage driving method, such as having a higher initial voltage pulse than the required working sustaining voltage, so as to achieve a faster liquid crystal response time. However, this particular method, although having reduced rise time, does not however make any significant improvement to the fall time; and at the same time it also has a complicated driving pattern, thereby leading to higher costs due to requiring a more complicated driving circuit for mobile device applications.
According to Reference 1: Optical Review, Vol. 6, pp. 471 (1999), which recites as follows: “[t]he thickness of the LC layer becomes extremely large at the center region of a convex lens-cell or at the peripheral part of a concave lens-cell, however, in comparison with that of a usual conventional LC display. This makes the response and recovery properties in this LC lens when applying and removing the driving voltage very slow. In addition, the transmission of incoming light is reduced according to the increase in thickness of the LC layer due to the absorption and/or scattering effect.” Therefore, the disadvantages of conventional LC lens system include at least, for example, excessive thickness, slower response time, and reduced light transmission rate. In addition, Reference 2: Applied Optics, Vol. 45, pp. 4576 (2006) recites as follows: “[o]ne of the fundamental problems in the development of electrically controlled NLC lenses is their slow response. The NLC lens needs to be relatively thick for the sufficiently wide range of focus changes. However, by increasing the thickness d of the lens, one significantly increases the time needed for director reorientation, as . . . .” In other words, the disadvantages of conventional electrically controlled LC lens in regard to their slower response time and relatively thick lens for covering a wide range of focus changes are further taught in Reference 2. Moreover, Reference 3: Molecular Crystal and Liquid Crystals, Vol. 433, pp. 229 (2005) recites as follows: “[t]he thickness of the LC layer in an LC lens usually exceeds 100 μm and therefore the operation of an LC lens is generally very slow . . . .” In other words, Reference 3 teaches that the thickness of the LC layer is usually over 100 microns in thickness and it is thereby also too slow.
According to Reference 4: IEICE Trans. Electron., Vol. E91-C, 1599 (2008), which it recites as follow: “ . . . , and is hopeful to be used in imaging systems, such as cell phone cameras and web cameras In this paper, the using of the LC lenses as focusing elements in image formation systems including a relay lens scope . . . ” and “[i]t would be better if the aperture of the LC lens was equal to or larger than that of the TV lens (27 mm), but the focus range of an LC lens is inversely proportional the aperture area . . . ”. Therefore, Reference 4 teaches that the focus range is inversely proportional to the aperture area, and that the recommended aperture should be equal or larger than 27 mm. Meanwhile, according to Reference 5: Optics Communications, Vol. 250, pp. 266 (2005) which recites: “ . . . various kinds of structures have been proposed. The operation of an LC lens is generally very slow, which limits its applications in many areas . . . ”, the shortcomings of the conventional LC lens with respect to slower response time are further illustrated.
Notwithstanding, it is known in the conventional art, for example, that the LCs have very slow response to external field, which is found, for example, in Reference 6: Jpn. J. Appl. Phys., Vol. 40, pp. 6012 (2001), which recites as follows: “[a]s is well known, although LCs have large optical and electrical anisotropies, which make them excellent optoelectronic materials, their response to external electric fields is extremely slow . . . .”
Teaching away from the use of hole-patterned design for LC lens systems is also evidenced, for example, in Reference 7: Jpn. J. Appl. Phys., Vol. 41, pp. L1232 (2002), which recites as follows: “[t]he problems associated with these LCLs are that either disclination lines occur easily, the operating speed is low, the size is too small, the optical quality is poor, or the adjustable parameters for quality improvement have not been defined.”
As can be seen from many of the above cited references, operating issues such as slower response time, reduced light transmission, and/or excessive LC layer thickness as met by the conventional LCs systems have rendered them unable to meet the demands for commercial autofocusing digital camera modules for achieving adequate image quality within a focus range from 10 cm to infinity.